1. Field of the Invention
The present invention relates to a semiconductor manufacturing method which provides epitaxial growth and the like on the surface of a silicon substrate placed in, for example, a reaction chamber, by using reactive gas (corrosive gas).
2. Description of the Related Art
Manufacturing processes for providing a semiconductor circuit such as an LSI on a silicon substrate include selectively and epitaxially growing a silicon thin-film on the surface, providing a pattern comprising an SiO2 film (silicon oxide) on the surface of a silicon substrate W, and epitaxially growing a silicon film in a region where the silicon is exposed, vapor-depositing a single-crystal silicon thin-film (epitaxial layer) having a predetermined concentration of impurity on a substrate for a MOS device comprising a silicon substrate having extremely low resistivity, and the like.
In these manufacturing processes, the silicon substrate is placed inside a process chamber and a reactive source gas is injected therein to grow the epitaxial layer on the substrate.
Other manufacturing processes using reactive gas include a variety of CVD processes for providing a thin-film on a substrate by the reaction of the reactive gas, and etching processes for providing micro-patterns, etc.
The reactive gas used in these semiconductor manufacturing apparatuses comprises a corrosive gas, such as ultra-high purity hydrogen chloride gas or ammonia gas. However, when the gas contains even a small amount of moisture, the metal components used in the apparatus (e.g. in the process chamber, gas supply system, gas discharge system, etc.) become susceptible to corrosion. This leads to hazardous pollution caused by metal (heavy metal) from the metallic sections. Consequently, there is a demand for a highly sensitive method for quantitative analysis of the moisture in corrosive gas inside the process chamber.
Conventionally, the only means of investigating the interrelation between processing conditions and heavy metal pollution, and the interrelation between processing conditions and the characteristics of the reactive gas processing, has been to feed back results obtained by directly analyzing a processed monitor wafer by using chemical analysis (atomic absorption spectrometry, radioactivation analysis, etc.), physical analysis (SIMS, TXRF, etc.), and electrical analysis (DLTS, SPV, lifetime, etc.).
In recent years, means for measuring the moisture content in reactive gas (corrosive gas) comprising a laser moisture measuring device which radiates laser light into the main body of a tube-like cell, connected to a process chamber, and measures the absorption spectrum of the transmitted light, has been proposed in, for example, Japanese Unexamined Patent Application, First Publication (Kokai), No. Hei 5-99845, Japanese Unexamined Patent Application, First Publication (Kokai), No. Hei 11-183366 and the like. Since the laser moisture measuring device can measure the gas without contact with the gas, it can measure even, reactive gas with high precision. Therefore, it has become possible to measure the moisture content inside the process chamber even during processing.
However, the conventional semiconductor manufacturing technology described above does not address the following problems. During the actual processing, the moisture content inside the process chamber is not always constant in each process. Even when conditions are set after feeding back the results of analysis of the process monitor wafer, fluctuation in the moisture content causes variation in the characteristics of the reactive gas processing. For example, in the case of the selective epitaxial growth already mentioned, the moisture (absorbed moisture) of the SiO2 film may be removed during pre-processing baking of the substrate, whereby the moisture content inside the process chamber increases. In this case, the moisture content increases during selective epitaxial growth, affecting the characteristics of the selectability of the selective growth and the selectively deposited film.
Furthermore, the moisture within the process chamber does not come only from the reactive gas pipes, and may be caused by atmosphere seeping in from other outside regions. This also increases the moisture content, making it difficult to determine the cause of fluctuations in the moisture content merely by measuring the moisture content in the process chamber. Nor is it clear what level of moisture content within the process chamber will make it possible to adequately control the effects of heavy metal pollution. For example, as shown in FIG. 9, an investigation of the relationship between the recombination lifetime and the moisture of discharged gas during the reaction reveals that the lower the moisture content, the longer the lifetime. However, there is a considerable difference between the average lifetime (solid line) and the maximum lifetime (broken line). This is due to spots of heavy metal pollution on the surface of the substrate.